High frequency generators, which are exemplified by radiofrequency (RF) generators, and related electrodes are commonly used in the treatment of pain and neurological diseases. Examples are the equipment and applications of Radionics, Inc., Burlington, Mass., such as the RFG-3C RF Lesion Generator and related electrode systems. Related information is provided in the paper by Cosman, E. R. and Cosman, B. J. entitled “Methods of Making Nervous System Lesions,” in Wilkins R H, Rengachary SS (eds): Neurosurgery. New York, McGraw-Hill, Vol. III, 2490-2498, 1984, and is hereby incorporated by reference herein in its entirety. The Radionics brochures on the TIC Kit, TEW Kit, Gildenberg Stereotaxy Kit, and SMK Kit contain related information, and they are hereby incorporated by reference herein in their entirety.
U.S. patent application Ser. No. 11/355,960 entitled “Integral High Frequency Electrode” in the name of Eric R. Cosman, Sr. and Eric R. Cosman, Jr. describes a unitized high frequency electrode system with non-separable cable and injection components in various examples, and is hereby incorporated by reference herein in its entirety.
The U.S. patent entitled “Universal Lesion and Recording System” by Eric R. Cosman, U.S. Pat. No. 4,565,200, issued Jan. 21, 1986, describes a high frequency electrode system having an electrode that is adjustable with respect to an insulated cannula that thereby achieves variability in the length of the uninsulated electrode tip for both a straight electrode geometry as well as a flexible side-issue electrode tip geometry. That patent is hereby incorporated by reference herein in its entirety.
The Radionics TEW Kit is a commercial example of an implementation related to the above-mentioned U.S. Pat. No. 4,565,200. It includes an insulated metal tubing that is rigid. A separated RF electrode is inserted into the insulated metal tubing, and the uninsulated tip of the electrode emerges from the insulated tubing distal end. A straight electrode, as well as a flexible side-issue electrode, is included in the TEW Kit. Continuous variation of the exposed uninsulated tip length is achieved by varying the insertion depth of the electrode in the metal tubing cannula. The extent of uninsulated tip length is adjusted continuously and clamped by a setscrew on the proximal hub of the insulated metal tubing. One disadvantage is that the insulated metal tubing or cannula is straight. It is sometimes clinically desirable to have a permanent rigid, curved distal tip to an electrode or an insertion cannula for steering the electrode or cannula into the patient's body toward a desired target tissue. Another disadvantage is that the cannula of the TEW Kit is a metal tubing with an insulating coating fixed to the cannula and covering the cannula. This increases the overall diameter of the cannula and insulation combination. Another disadvantage is that the RF electrode which slides inside the insulated cannula is of a smaller diameter than the outside insulated cannula, which decreases the heating region of the electrode system for a given overall shaft diameter. Another disadvantage is that the insulating element is the outer metal tubing with its insulating covering. This is not flexible as compared to for example, an insulating sleeve that is made entirely of an insulating material, such as a plastic sleeve. Another disadvantage is that the TEW Kit components are complex and expensive to make. The insulated cannula is first inserted into the patient's body with an obdurating rigid stylet inserted into it. Once in place, the stylet is removed and the electrode, either straight or curved variety, is inserted into the cannula. This multi-step procedure increases surgery time and expense. Another disadvantage is that the TEW system does not have discrete, uninsulated electrode tip lengths at fixed finite values, but rather has a continuous range of tip exposures that are set by the setscrew. This requires more deliberate attention by the surgeon to set a desired tip length.
The Radionics TIC Kit includes four insulated cannulae with different tip exposures. The clinician decides before the procedure which length of tip exposure is desirable. One disadvantage is that the TIC Kit requires four different cannulae for the four available tip exposures. This makes the TIC Kit more complex and more expensive.
The U.S. patent entitled “Adjustable Transurethral Radiofrequency Ablation” by Eric R. Cosman and Francis J. McGovern, U.S. Pat. No. 6,743,226 D2, issued Jun. 1, 2004, describes an RF catheter system with an exposed electrode that comprises metal rings around the distal end of a urethral catheter. The length and configuration of unexposed electrode surfaces can be adjusted by changing the degree of insulation coverage of the metal electrode rings. In one example, this is achieved by removal of insulated bands that are placed on indiscrete positions on the rings so as to expose more electrode surface at desired positions. In another example, the degree of uninsulated electrode exposure can be changed by movement of an insulated sleeve over the ring. One disadvantage of these systems in the context of pain treatment is that the catheter is not rigid and therefore cannot be inserted into the skin and the patient's bodily tissues in a self-supported manner. Another disadvantage is that the system configuration cannot be used easily for percutaneous insertion of electrodes into the back near the spine or into the brain, or into other target tissues such as cancerous tumors, making the system poorly configured for applications of pain therapy or tumor therapy.